This paper investigates the use of clonal selection principles based on our immune system for optimization applications in electromagnetics. This concept is based on our immune system's ability to respond to an antigen and produce a pool of anti-body secreting cells. In addition to the common implementations of this algorithm where the affinity maturation and cloning principles of clonal selection principles are used, we utilize memory and the cross-over concepts that are common to other bio-inspired methods. The performance of the algorithm is investigated for well known mathematical test functions and its potential is demonstrated in the context of the design of a radar absorbing material and a planar phased array antenna with specific radiation and null characteristics.

An improved Central Force Optimization (CFO) algorithm for antenna optimization is presented. CFO locates the global extrema an objective function to be maximized, in this case antenna directivity, by flying "probes" through the decision space (DS). The new implementation includes variable initial probe distribution and decision space adaptation. CFO's performance is assessed against a recognized antenna benchmark problem specifically designed to evaluate optimization evolutionary algorithms for antenna applications. In addition, summary results also are presented for a standard twenty-three function suite of analytic benchmarks. The improved CFO implementation exhibits excellent performance.

A new miniaturized bandpass fractal frequency selective surface (FSS) with excellent angular stability performa nce is proposed. The minia turization has been achieved by scheming out a symmetric fractal pattern of continuous slots from the surface of a square-shaped patch, in which each periodic cell consists of incurved slot resonator for reducing the cell size. Reduction in FSS size of up to 74% with respect to the conventional square loop aperture FSS operating at the same frequency of 3.3 GHz is obtained. Furthermore, results show excellent angular stability for both vertica land horizontal polarization at different incidence angles because of its fractal configuration. A prototype is fabricated and the FSS measurement, and simulation results are presented and discussed.

To predict the three-dimensional radar cross section (RCS) pattern of an arbitrary shaped perfectly electric conductor objects in both a broad frequency band and angular domains simultaneously, the method of moments (MoM) combined with the Chebyshev polynomial approximation is presented. The induced current is expanded by a bivariate Chebyshev series. Using this function, the induced current can be obtained at any frequency and angle within the desired frequency band and angular domains. Numerical results show that the proposed method is found to be superior in terms of the CPU time to obtain the three-dimensional RCS pattern compared with the direct solution by MoM repeating the calculations at each frequency and angle. Good agreement between the presented method and the direct MoM is observed.

We have proposed a new architecture for an array in which the elements are placed on a spiral curve in order to obtain an ultra wideband (UWB) radiation pattern. In addition, array factor and bandwidth of the proposed spiral array are calculated. Simulated results obtained by SuperNEC and CST software have shown good agreement with the analytic calculations. Although the proposed antenna array is wideband in nature, it lacks desirable efficiency, due to poor front to back ratio (FBR) and sidelobe level (SLL). In this paper, we have chosen three different approaches in order to improve the e±ciency of proposed array. First, the effect of length and thickness tapering of elements has been studied. Second, we have used Genetic Algorithm (GA) to optimized pattern shape. Finally, the influence of metamaterial cover on array performance has been investigated. Although the first and second methods improve the radiation pattern, the array bandwidth is reduced. It is shown that the third method improves array directivity and FBR by 5-7 dB and 15-17 dB respectively within the frequency band of operation.

Holey fibers (HF) with their peculiar properties have been used in fabrication of Erbium doped holey fiber amplifiers (EDHFA) for third optical communication window. In this paper, by using scalar effective index method, the analyses are presented to investigate the effects of HF geometrical parameters on the gain performance of the EDHFAs. The hierarchical variations of the parameters, including the air-hole sizes (AHS), propagating modes of the core and cladding, mode field diameter of the signal and pump, would cause alterations in the maximum gain and the optimum lengths of the EDHFAs. By determining the normalized frequency of the HF in wide range variations of the air-hole diameter, air-hole spacing, and air-filling factor (AFF), the single-mode regions for signal and pump wavelengths are obtained, where the maximum gain and the optimum lengths are evaluated. In addition, the influence of pump power and the dopant concentration in terms of the AFF are investigated. It is shown that by using suitable AHS and AFF, one can obtain a higher gain for a shorter optimum length in the EDHFAs. The obtained results can be a useful tool for design of HF-based optical amplifiers with lesser effects of amplified spontaneous emission and nonlinearities because of shorter optimized length.

In this paper, a folded stepped impedance resonator (SIR), modified by adding an inner quasi-lumped SIR stub, is used as a basis block for a new implementation of dual-band bandpass filters. The main advantage of the proposed filter is to make it possible to independently control the electrical features of the first and second bands. The behavior of the first band basically depends on the geometry of the outer folded SIR. The second band, however, is strongly influenced by the presence of the inner stub. Additional design flexibility is achieved by allowing the inner stub to be located at an arbitrary position along the high impedance line section of the main SIR. The position of the tapped input and output lines can be optimized in order to reach a reasonable matching of the filter at the central frequencies of both passbands. Some designs are reported to illustrate the possibilities of the proposed structure. Experimental verification has been included.

The frequency responses of two widely used active inductor topologies are analyzed and compared using a generalized circuit model for the active devices in the circuits. A very wideband active inductor in CMOS was subsequently fabricated and tested and the inductor exhibits a measured self-resonant frequency of 9.7 GHz.

This work investigates the variation of the real part of the complex magnetic permeability of a Ni-Zn ferrite for application to temperature sensors. Ferrite samples were fabricated by means of the conventional ceramic method. Zinc, nickel and iron oxides were used as raw materials. The samples were sintered at 1200, 1300, and 1400^oC. The complex magnetic permeability of the samples was measured at temperatures ranging from -40^oC to +50^oC. The complex magnetic permeability of the samples was analyzed in the 100 kHz--100 MHz frequency range, and the temperature sensitivity of the magnetic permeability (μr'/T) was analyzed at 100 kHz. The magnetic permeability variation of the ferrite permits to use it as a temperature transducer with a maximum temperature sensitivity of about -119^oC^-1. The highest magnitudes of temperature sensitivity occurred between +30^oC and +50^oC. Therefore, the ferrite could be sensitive enough to allow temperature measurements at the human body temperature level. The results indicate that the temperature range of maximum temperature sensitivity of the ferrite may be adjusted by means of appropriate selection of the fabrication parameters.

In this paper a novel method for crosstalk reduction is proposed. This is achieved through using the step shaped transmission line, which basically attempts to create steps along the transmission lines to decrease the crosstalk, while having negligible variation in return loss. To this end, various simulations are carried out to get an intuition regarding the underlying processes conducted to the far-end crosstalk, thereby enabling to optimize the far-end crosstalk, and simultaneously to yield a small variation in the return loss. Accordingly, a conventional coupled transmission line is employed as a benchmark, enabling to have an idea regarding the impact of the proposed method in terms of the ability to decrease the far-end cross talk. Furthermore, the proposed transmission line and the benchmark structure are fabricated and then evaluated to verify the experimental results to that of the simulation. In addition, comprehensive parametric studies have been carried out to get insight on the effect of various adjustable parameters over the crosstalk. The obtained results show that the crosstalk is decreased more than 4 dB over the entire operating bandwidth. Some advantages such as ease of design and fabrication have made the proposed technique an advisable method when dealing with low crosstalk.

A new reciprocal heuristic diffraction coefficient for lossy dielectric wedge is presented which is applicable to arbitrary positions of transmitter and receiver in a complex channel environment. The prediction obtained using proposed coefficient is compared with those obtained using rigorous Maliuzhinets'solution. The comparison shows significant improvement over available heuristic coefficients. The coefficient is valid for both parallel and perpendicular polarizations. Further, the measurement of the electric field in the vicinity of edge of the building is carried out, and the measurement result, thus obtained, is compared with predictions using the proposed coefficient.

In this paper, a novel band-notched circular slot (BNCS) antenna for ultra-wideband (UWB) communication is proposed. This antenna is comprised of a circular stub that excite similar-shaped slot aperture. The proposed antenna is designed on the RO4350B substrate with thickness of 500 μm and relative permittivity (ε_r) of 3.4 to operate in UWB band released by the US's Federal Communications Commission (FCC) in 2002 (i.e., 3.1-10.6 GHz). To reject the frequency band of 5.15-5.825 GHz, which is limited by IEEE 802.11a and HIPERLAN/2, an inverted-cup strip is parasitically attached to the feed layer. The size of our proposed antenna is 50×50 mm², and this antenna has good radiation characteristics. Effects of varying the parameters of parasitic inverted-cup strip on performance of the proposed antenna have been studied. The antenna with optimal parameters obtained from parametric study is fabricated and measured. It is observed that the simulated and experimental results have good agreement with each other.

Relationships between the properties of surface waves in radar absorbing materials (RAM) layers and mono-static radar cross section reduction (RCSR) performances of a coated slab are studied. In this paper, two kinds of RAM were employed for double-layer coating. By changing the thickness of each layer and the order of RAMs, mono-static RCSR performances of the coated slab are studied. Simultaneously mono-static RCSR performances of a slab coated with equivalent medium of the considered RAMs in situ are calculated and compared with the previous ones in regard to the properties of surface waves. It is found that surface waves in between layers for various coated projects can be evaluated. Our results suggest that the optimal coated order for RAMs exists, and the method may be efficient for coating strategy with various kinds of RAMs. Electromagnetic scatterings of the equivalent medium exclude the effect of surface waves in between layers. Therefore, the equivalent medium theory is not appropriated for the research of electromagnetic scattering on lossy mediums.

A Dual band Microstrip Antenna Arrays (DbMSAA) incorporated with Mushroom Electromagnetic band Gap (MEBG) and modified Minkowski Electromagnetic Band Gap structures to further improve its radiation characteristics is reported in this work. The two different types of EBG structures work like a Band Rejecter (BR), separating the branch of feed line feeding two different groups of patch antenna arrays operating at 2.4 GHz and 5.8 GHz, thus making them operate individually at their particular frequencies, simultaneously. Initially, the possibilities of having a uniform and controlled radiation patterns are quite complicated to achieve due to the single port feeding technique used and developments of grating lobes at the higher band frequency, but, through the incorporation of the EBG structures, the problems could be solved immediately. The antenna's performance is improved where the grating lobes at 5.8 GHz are diminished, and the radiation patterns of the dual band antenna at both frequencies become more symmetrical with increased gain.

A novel compact resonator for LPF is proposed in this paper. It is composed of a circular hairpin resonator and a pair of coupled parallel stepped impedance resonators (SIRs) inside. With the loaded SIRs, additional two transmission zeros can be introduced and adjusted easily to cancel the spurious responses for stopband extending, while do not change the filter size. Filters using one and two of the new cells were designed and measured. The two-cell LPF has an insertion loss less than 0.6 dB from DC to 1.6 GHz, including attenuation of double SMA transitions at both sides of the circuit which is about 0.3 dB, and a wide -10 dB stopband from 2.5 to 13 GHz (corresponding to 146% normalized 10 dB stopband), but has a size of only 0.129 λg × 0.073 λg.

Comparing with an all-dielectric binary photonic crystal, we show, in this work, that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged. First, the band gap enlargement due to the addition of the metallic film is examined in the case of normal incidence. Next, in the oblique incidence, a wider omnidirectional band gap can be obtained in such a ternary metal-dielectric photonic crystal. All the theoretical analyses are made based on the transfer matrix method together with the Drude model of metals.

This paper presents a CPW-fed planar inverted cone antenna (PICA) for ultra-wideband (UWB) communication applications. The proposed PICA provides a conventional monopole type omnidirectional radiation pattern, and it utilizes the advantages of the coplanar-waveguide (CPW) to simplify the structure of the antenna into a single metallic level. To improve radiation characteristics, a tapered and corrugated ground plane is used. In addition, the PICA's radiating element with three self-similarity holes is attempted to enhance performance of the antenna. The simulated and measured results demonstrate that the proposed PICA achieves a broad impedance bandwidth from 1.3 GHz to 11GHz within the magnitude of S₁₁ (dB) less than -10 dB and maintains nearly omnidirectional radiation characteristics.

This paper presents the design of a novel dual-band unequal Wilkinson power divider. The proposed power divider can operate at arbitrary two frequencies without reactive components. The design and analysis of power divider are presented. The structure of the power divider and the formulas used to determine the design parameters have been given. Closed-form design equations are derived based on network theory. For verification, a microwave power divider operating at 1 and 2 GHz is fabricated, the experimental results show that the designed unequal power divider fulfills all the features of a conventional Wilkinson power divider.

The backscattering experiments of water surface by Ultra-High Frequency (UHF, 300 ~ 3000 MHz) Radar are presented in this paper. In order to study UHF radio propagation and backscatter mechanisms from fresh and salty water surfaces at a very low grazing angle, two experiments are carried out on Yangtze River bridge and cliff which face open sea with the same radar system. The physical parameters of different water surfaces are introduced as well as the signature of backscattered echoes.

Novel time-harmonic beam fields have been recently obtained by utilizing a non-orthogonal coordinate system which is a priori matched to the field's planar linearly-phased Gaussian aperture distribution. These waveobjects were termed tilted Gaussian beams. The present investigation is concerned with parameterization of these time-harmonic tilted Gaussian beams and of the wave phenomena associated with them. Specific types of tilted Gaussian beams that are characterized by their aperture complex curvature matrices, are parameterized in term of beam-widths, waist-locations, collimation-lengths, radii of curvature, and other features. Emphasis is placed on the difference in the parameterization between the conventional (orthogonal coordinates) beams and the tilted ones.